1. Field of the Invention
This invention generally relates to a motor rotor, and more specifically, to a motor rotor that adopts magnetic force.
2. Description of Related Art
Motors convert electric energy to mechanic energy, thereby providing output rotational motions; and in addition to directly providing rotational motions, output rotational mechanic energy can also work with various mechanisms and then convert into linear motions or vibratile motions.
A motor that provides rotational motion consists of motor and stator, wherein the stator is a portion for fixing and providing ambient magnetic field, while the rotor is a portion that is rotatable in response to the magnetic field. A common rotor comprises a turning axle and a plurality of magnetic members, e.g. permanent magnets, wherein the turning axle is made of a plurality of magnetically permeable elements, e.g. stacked silicon steel sheets, and the magnetic members are circumferentially disposed on the peripheral wall surface of the turning axle.
Taking permanent magnets as an example, glue is commonly applied to between the turning axle and the permanent magnets, e.g. resin glue, for fixing in position the permanent magnets to the turning axle. However, since permanent magnets are fixed in position to the turning axle by means of gluing, the permanent magnets are likely to fall off as a result of the effects of external usage surroundings and/or pressure. Once the permanent magnets fall off, the motor rotor will definitely be incapable of rotating normally, and even worse, the permanent magnets may be stuck in the stator.
Common factors of external surroundings that cause the foresaid falling-off of permanent magnets include, but are not limited to, temperature and humidity. Where ambient temperature at which the motor works changes dramatically, e.g., in the frigid zone, where temperature is below zero, since coefficients of thermal expansion of permanent magnet and silicon steel sheet are different, delamination is likely to happen due to difference in size variation; in addition, when motor usage surroundings humidity is changing dramatically, e.g. under water or in a humid area, since silicon steel sheet is likely getting rusty and accumulating rust, and the rust is pushing away the glue layer (solidified glue) and eventually causing delamination. Although the aforesaid effects of the factors of external surroundings are not attributable to the quality of the motor, as a matter of fact, the aforesaid effects indeed directly shorten the life of the motor; therefore, it is an urgent issue in the motor industry as to how to overcome the drawback of a shortened life span of motors caused by external surroundings factors.
In order to overcome the drawback of a short life span of motors caused by the gluing technique, the prior art is cited herein, including Taiwanese Patent No. 595072, Taiwanese Patent No. 579131, Taiwanese Patent No. 412100, Taiwanese Patent No. M302825, and Patent No. M312835, etc.
In general, manufacturers adopt designs of assembly to assemble a turning axle and permanent magnets. The most common adopted designs of assembly is characterized by forming a plurality of equidistantly spaced coupling slots on the peripheral wall surface of a turning axle, and each of the coupling slots is coupled with a corresponding permanent magnet. However, since silicon steel sheets and permanent magnets are made by different fabrication techniques, their fabrication precision are of different levels, thereby causing a great deal of variations in assembly combinations. The variations in assembly combinations frequently further cause the fragile permanent magnets to crack while coupling with the coupling slots in the assembly process, thereby leading to poor yield in the assembly process.
Taiwanese Patent No. 412100 disclosed a motor rotor, wherein a turning axle is formed by stacking a plurality of silicon steel sheets, and then a plurality of equidistantly spaced fixing slots are disposed on a peripheral wall surface of the turning axle. Each of the fixing slots receives a fastening bolt, and any two neighboring fastening bolts are coupled with a permanent magnet within the two neighboring fastening slots; and each end of the turning axle is disposed with an end cover plate for fixing in position the permanent magnets and the fastening bolts to the turning axle, thereby preventing the permanent magnets and the fastening bolts from falling off either end of the turning axle.
In the foresaid patent, in order to engage the permanent magnets to the turning axle, two additional fastening bolts are disposed for each of the permanent magnets; and in order to correct a matching error related to fabrication precision, two additional end cover plates are further provided; thereby not only increasing cost of assembly elements and assembly process and stockpile, but also reducing the yield greatly. In addition, since stamping precision level of forming fixing slots on silicon steel sheets is at least double compared with fabrication precision level of permanent magnets, assembly precision is unlikely to be controlled well, and clearance fit or interference fit commonly happens to assembly relation. In case of interference fit, a penetrating fastening bolt pushes and impacts the permanent magnet and thereby directly cracks and damages the permanent magnet, thereby seriously affecting the yield and keeping production costs high.
According to the Taiwanese Patent No. 595072, a motor rotor is provided, wherein the motor rotor comprises a turning axle, a plurality of permanent magnets, and inserting small teeth; the turning axle is wholly made of silicon steel instead of stacking a plurality of silicon steel sheets as shown in structure design of prior art; a plurality of coupling bumps equidistantly spaced apart from one another are circumferentially formed on the peripheral wall surface of the turning axle, and each of the permanent magnets is correspondingly disposed between the two neighboring coupling bumps circumferentially formed on the peripheral wall surface of the turning axle, and then correspondingly inserting an inserting small tooth with a corresponding coupling groove into each of the coupling bumps, thereby holding and fixing in position each of the permanent magnets by two neighboring inserting small teeth.
However, each of the foresaid inserting small teeth must be fabricated according to size and shape of the permanent magnets. Moreover, each of the coupling grooves must be fabricated in accordance with shape and size of each of the coupling bumps, and obviously demanding higher fabrication technique and precision level. Besides, a great deal of the inserting small teeth are required, not only increasing costs of elements, assembly, and stockpile, but also leading to poor fixation. The inserting small teeth must tightly contact with the permanent magnets to ensure effective fixation. However, fabrication precision errors continue and end up with a cumulative count. Therefore, the permanent magnets are susceptible to vibration and looseness which are even more severe in the presence of the abovementioned external surrounding factors or pressure.
Taiwanese Patent No. 579131 disclosed a coupling fixing motor rotor comprising: coupling grooves formed inside exiting magnetic grooves of magnetically permeable elements of a turning axle; a coupling flange formed on an inner rim of an opening end of each of the coupling grooves; auxiliary positioning elements corresponding in shape to the magnetically permeable element and adapted for coupling and hooking up to each other, wherein the auxiliary positioning elements are long enough to couple and hook up with only one end of the permanent magnets but are absent from the magnetic grooves nor disposed between the permanent magnets.
However, the prior art entails tapering the permanent magnets functioning as magnetic members such that the permanent magnets can be pressed down and fixed in position to each of the coupling grooves, thereby allowing stress to focus on end of the permanent magnet; but for those permanent magnets made from micro particles by powder metallurgy, when stress is concentrated on end, it is likely to cause the end to crack, thereby ruining fixing effect; in addition, when the technique is adopted, a grinding wheel is commonly applied for sharpening ends of the permanent magnets, it is unlikely to obtain a preferable matching level between the permanent magnets and the coupling grooves, thereby leading to poor fixing effect and further decreasing the yield of motor rotors.
Taiwanese Patent No. M302825 disclosed a permanent magnet rotor structure, wherein dovetail tenons are formed on bottom surface of permanent magnets, and corresponding dovetail mortises are formed on a peripheral wall surface of a turning axle for correspondingly coupling with the permanent magnets; however, the patent here has same drawback shown in the claims of Taiwanese Patent No. 579131, which incapable of providing preferable fixing effect, and it is obviously more difficult in achieving the fabrication technique and precision demand.
A magnetic fixing device for motor is disclosed according to Taiwanese Patent No. M312835, wherein permanent magnets are held between two hollow pressing rings, one of the two hollow pressing rings has a plurality of protruding posts formed on its ring surface and equidistantly spaced apart from one another, the protruding posts each comprise two coupling portions on both lateral surfaces respectively and a fixing hole between the two coupling portions, and the other hollow pressing ring comprises axial fixing holes; also each of the permanent magnets has coupling portions on both lateral sides corresponding in position to the coupling portions for correspondingly coupling to between two neighboring protruding posts, and a plurality of fastening elements, e.g. screws, are applied separately to correspondingly run through each of the fixing holes, thereby fixing in position and integrating the hollow pressing rings to one entity, and fixing in position and clipping the permanent magnets between the two hollow pressing rings.
However, screws are applied to the prior art, and screws are likely to be magnetically permeable and consequently affect magnetic fields; besides, applying screws needs tool, and a great deal of amount of screws needed for assembly, thereby costing more time and energy and consequent inconvenience in fabrication process. Besides, eight screws are required according to the prior art, and in order to balance center of gravity, screws applied in assembly must be of same weight, and likewise corresponding nut applied; therefore, choosing of elements is very critical, and even inside a same batch, commonly there are elements of different weight; also a specific technique and procedure must be adopted for purpose of selecting proper elements, thereby increasing fabrication time and cost; moreover, motor rotor must keep rotational motions alive while operating, and the continuous rotational motions and vibrations together are very likely to loosen up the screws, consequently causing displacement of the permanent magnets and affecting usage life spans of motor and motor rotor.
Furthermore, the prior art disclosed a permanent magnet functioning as a magnetic member, between two neighboring posts, in other words, only applicable to motor rotors that have permanent magnets equidistantly spaced apart from one another, but not applicable to motor rotors that have permanent magnets coupled to one another, for instance, motor rotor shown by FIG. 1 in the specification of Taiwanese Patent No. 484766, thereby limiting application scope of the prior art.
In view of the abovementioned drawbacks of the prior art, it is a highly urgent issue in the industry as to how to provide a technique for fabricating motor rotor, which is capable of ensuring fixing effect, reducing elements of assembly, simplifying structure, providing easy assembly process, preventing usage life spans of motor and motor rotor from being affected by external surroundings factors, preventing magnetic members from cracking, and also enhancing the yield.